1. Field of the Invention
The present invention relates to a focusing device and a telescopic tube module thereof, and more particularly, to a focusing device and a telescopic tube module thereof for use with optical equipment such as telescopes or microscopes.
2. Background of the Invention
Telescopes are commonly used for many different purposes and by many different kinds of people, from amateur stargazers and enthusiasts catching a glimpse of astrological phenomena, to scientists conducting academic research. A telescope has a focusing device for adjusting an image of a viewed object, such as a star or a migratory bird, to the focus position of the telescope. As such, the viewed object can be seen distinctly. Therefore, the stability and the precision of the focusing device determine the quality of the telescope.
FIG. 1 and FIG. 2 show a conventional focusing device including a seat assembly 30, a shaft 31, two turn-knob mechanisms 32, a sleeve assembly 33, and a telescopic tube 34. The seat assembly 30 includes a seat (not labeled). The shaft 31 is pivotally disposed in the seat. Inner ends of the two turn-knob mechanisms 32 are respectively assembled on two ends of the shaft 31 and pivotally disposed in the seat. The sleeve assembly 33 includes a sleeve (not labeled). The sleeve is assembled on the seat. The telescopic tube 34 is slidably disposed in the sleeve. The focusing device is assembled in optical equipment such as telescopes and corresponds to an optical axis of an objective lens assembly of the telescope. When focusing, one of the turn-knob mechanisms 32 is rotated, so that the shaft 31 drives the telescopic tube 34 to move back and forth.
As the seat assembly 30 and the sleeve assembly 33 of the above conventional focusing device need to be manually assembled, the number of components thereof is increased and rather complex. As a result, errors in assembly are more likely, costs are increased, and the appearance of the focusing device less attractive. Maintenance work is also more costly and time-consuming.
FIG. 3 and FIG. 4 show another conventional focusing device including a base module 40 and a telescopic tube 47. The base module 40 includes a housing 41, a shaft 42, two turn-knob mechanisms 43, a support plate 44, two support elements 45, and at least two bearings 46. The housing 41 has an inner surface (not labeled) and a passageway (not labeled) formed in the inner surface. The shaft 42 is pivotally disposed in a bottom portion of the housing 41 and perpendicular to a longitudinal axial direction of the passageway. The shaft 42 has a part located in the passageway. The two turn-knob mechanisms 43 have inner ends being respectively assembled on two ends of the shaft 42. The support plate 44 is disposed between the bottom portion of the housing 41 and the shaft 42. The two support elements 45 are screwed in the bottom portion of the housing 41 and push the support plate 44 upward. The at least two bearings 46 are respectively and symmetrically disposed on an upper-left portion and an upper-right portion of the inner surface of the housing 41. The telescopic tube 47 is slidably disposed in the passageway along the longitudinal axial direction thereof. When focusing, one of the turn-knob mechanisms 43 is rotated, so that the shaft 42 drives the telescopic tube 47 to move back and forth.
The telescopic tube 47 is made of aluminum, and the shaft 42 and the bearings 46 are made of steel. When the two support elements 45 push the support plate 44 upward, the support plate 44 pushes the shaft 42 upward to contact the telescopic tube 47. As the hardness of the shaft 42 is greater than that of the telescopic tube 47, the telescopic tube 47 is compressed to form a rough and uneven surface. Also, as the hardness of the bearings 46 is greater than that of the telescopic tube 47, the telescopic tube 47 is compressed to form two concave lines. As a result, the stability and the precision of the focusing device are affected.
Still another conventional focusing device uses a mechanism of gears to drive its telescopic tube to move back and forth. However, there are gaps between the gears. Furthermore, vibrations greatly affect the stability and the precision of the focusing device.